The present invention relates to a fuel injection apparatus for an internal combustion engine, and more particularly to a fuel injection apparatus for an internal combustion engine employing a fuel injection pump having a variable pre-stroke mechanism, which fuel injection apparatus prevents damage to both the fuel injection pump and the internal combustion engine when trouble occurs in the control of the fuel injection pump.
The driving characteristics of an internal combustion engine can be improved by appropriate adjustment of the fuel injection rate. Because of this, in the prior art, there have been proposed various fuel injection pumps for internal combustion engines having a pre-stroke mechanism and enabling the fuel injection timing to be adjusted in addition to the fuel injection quantity, whereby the fuel injection rate can be set to a desired value (see, for example, Japanese Patent Application Disclosure No. 163169/84).
In an electronically controlled fuel injection apparatus which electronically controls injection quantity and injection rate and which uses this type of fuel injection pump, when there is a malfunction in the control circuit, it becomes impossible to detect the timing of the beginning of fuel injection. In other words, there is no way to obtain information on the state of regulation of the pre-stroke mechanism. Because of this, depending on the operating condition of the internal combustion engine at that time, the inner pressure of the cylinders of the internal combustion engine or the inner pressure of the injection pipes of the fuel injection pump may reach a greater value than is permissible. As a result, there is a high risk of damage to the internal combustion engine and the fuel injection pump. More specifically, when the amount of the pre-stroke is at its minimum due to a malfunction in the control system, the possibility of the inner pressure of the cylinders of the internal combustion engine being more than permissible occurs in the case where the speed of the internal combustion engine is high and the amount of fuel injection is great. On the other hand, when the amount of the pre-stroke reaches its maximum, the possiblity of the inner pressure of the injection pipes of the fuel injection pump being greater than permissible arises in the case where the speed of the internal combustion engine is high and the amount of fuel injection is great.
For eliminating the above-mentioned drawbacks, Japanese Patent Application Disclosure No. 63332/84 proposes an apparatus constructed so as to suppress the maximum fuel injection quantity when any trouble occurs in its control system. However, even if the maximum quantity of fuel injection is suppressed, the fuel injection timing will be in an advanced state at the minimum amount of pre-stroke, so that there is a danger of the internal combustion engine being damaged as a result of the inner pressure of the cylinders of the internal combustion engine becoming high.